On Mon 29-08-16 10:10:45, Johannes Weiner wrote:

On Tue, Aug 23, 2016 at 10:09:17AM +0200, Michal Hocko wrote:

quoted

From: Michal Hocko <mhocko@suse.com>

The current wording of the COMPACTION Kconfig help text doesn't
emphasise that disabling COMPACTION might cripple the page allocator
which relies on the compaction quite heavily for high order requests and
an unexpected OOM can happen with the lack of compaction. Make sure
we are vocal about that.

I find it weird to even have this as a config option after we removed
lumpy reclaim. Why offer a configuration that may easily OOM on allocs
that we don't even consider "costly" to generate? There might be some
specialized setups that know they can live without the higher-order
allocations and rather have the savings in kernel size, but I'd argue
that for the vast majority of Linux setups compaction is an essential
part of our VM at this point. Seems like a candidate for EXPERT to me.

I was thinking about making it depend on EXPERT as well but then I just
felt like making the text more verbose should be sufficient. If somebody
runs a kernel without COMPACTION and doesn't see any issues then why
should we make life harder for him. But I was thinking about a different
thing. We should warn that the compaction is disabled when the oom
killer hits for higher order. What do you think?
--- 

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 10f686969fc4..b3c47072a206 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c

@@ -406,6 +406,8 @@ static void dump_header(struct oom_control *oc, struct task_struct *p)
 	pr_warn("%s invoked oom-killer: gfp_mask=%#x(%pGg), order=%d, oom_score_adj=%hd\n",
 		current->comm, oc->gfp_mask, &oc->gfp_mask, oc->order,
 		current->signal->oom_score_adj);
+	if (!IS_ENABLED(COMPACTION) && oc->order)
+		pr_warn("COMPACTION is disabled!!!\n");
 
 	cpuset_print_current_mems_allowed();
 	dump_stack();

-- 
Michal Hocko
SUSE Labs

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>